diff --git a/README.md b/README.md index 64bea04..78da997 100644 --- a/README.md +++ b/README.md @@ -1,20 +1,13 @@ # varint -decode [protobuf-style varint bytes](https://developers.google.com/protocol-buffers/docs/encoding#varints) and emit whole integers when enough have been accumulated that a number can be constructed; also encode whole numbers to an array of varint style bytes. +encode whole numbers to an array of [protobuf-style varint bytes](https://developers.google.com/protocol-buffers/docs/encoding#varints) and also decode them. ```javascript var varint = require('varint') var bytes = varint.encode(300) // === [0xAC, 0x02] - , vi = varint() - -vi.once('data', function(num) { - console.log('got', num) -}) - -vi.write(bytes[0]) -vi.write(bytes[1]) // "got 300" - +varint.decode(bytes) // 300 +varint.decode.bytesRead // 2 (the last decode() call required 2 bytes) ``` ## api @@ -24,16 +17,22 @@ vi.write(bytes[1]) // "got 300" ### varint.encode(num[, output=[], offset=0]) -> array encodes `num` into either the array given by `offset` or a new array at `offset` -and returns that array. +and returns that array filled with integers. + +### varint.decode(data[, offset=0]) -> number + +decodes `data`, which can be either a buffer or array of integers, from position `offset` or default 0 and returns the decoded original integer. + +### varint.decode.bytesRead -### vi = varint() -> EventEmitter +if you also require the length (number of bytes) that were required to decode the integer you can access it via `varint.decode.bytesRead`. this is an integer property that will tell you the number of bytes that the last .decode() call had to use to decode. -return a new `varint` instance. +## usage notes -### vi.write(byte) -> undefined +if you are using this to decode buffers from a streaming source it's up to you to make sure that you send 'complete' buffers into `varint.decode`. the maximum number of bytes that varint will need to decode is 8, so all you have to do is make sure you are sending buffers that are at least 8 bytes long from the point at which you know a varint range begins. -write a byte to the varint. if the byte is "final" (i.e., does not have the bit at `0x80` set), -it will attempt to compile the number and emit it as a `data` event. +for example, if you are reading buffers from a `fs.createReadStream`, +imagine the first buffer contains one full varint range and half of a second one, and the second buffer contains the second half of the second varint range. in order to be safe across the buffer boundaries you'd just have to make sure the buffer you give to `varint.decode` contains the full varint range (8 bytes), otherwise you'll get an error. # License diff --git a/decode.js b/decode.js index 7e2530f..6269e73 100644 --- a/decode.js +++ b/decode.js @@ -1,33 +1,24 @@ -module.exports = Decoder +module.exports = read var MSB = 0x80 , REST = 0x7F - -function Decoder() { - this.accum = [] +function read(buf, offset) { + var res = 0 + , offset = offset || 0 + , shift = 0 + , counter = offset + , b + + do { + b = buf[counter++] + res += shift < 28 + ? (b & REST) << shift + : (b & REST) * Math.pow(2, shift) + shift += 7 + } while (b >= MSB) + + read.bytesRead = counter - offset + + return res } -Decoder.prototype.write = write; - -function write(byte) { - var msb = byte & MSB - , accum = this.accum - , len - , out - - accum[accum.length] = byte & REST - if(msb) { - return - } - - len = accum.length - out = 0 - - for(var i = 0; i < len; ++i) { - out |= accum[i] << (7 * i) - } - - accum.length = 0 - this.ondata(out) - return -} \ No newline at end of file diff --git a/encode.js b/encode.js index 3e68c02..e2e2e36 100644 --- a/encode.js +++ b/encode.js @@ -14,4 +14,4 @@ function encode(num, out, offset) { } out[offset] = num return out -} \ No newline at end of file +} diff --git a/index.js b/index.js index 68483bd..1c4e803 100644 --- a/index.js +++ b/index.js @@ -1,22 +1,4 @@ -module.exports = varint - -varint.encode = require('./encode.js'); - -var EE = require('events').EventEmitter - , Decoder = require('./decode.js') - -function varint() { - var ee = new EE - , dec = new Decoder - - dec.ondata = function (item) { - ee.emit("data", item) - } - - ee.write = function (item) { - dec.write(item); - } - - return ee -} - +module.exports = { + encode: require('./encode.js') + , decode: require('./decode.js') +} \ No newline at end of file diff --git a/package.json b/package.json index a7569cf..547046b 100644 --- a/package.json +++ b/package.json @@ -1,7 +1,7 @@ { "name": "varint", "version": "0.0.3", - "description": "use msb to create integer values of varying sizes", + "description": "protobuf-style varint bytes - use msb to create integer values of varying sizes", "main": "index.js", "scripts": { "test": "node test.js" diff --git a/test.js b/test.js index 812733b..58bd670 100644 --- a/test.js +++ b/test.js @@ -1,85 +1,72 @@ var varint = require('./index') , test = require('tape') + , decode = varint.decode + , encode = varint.encode test('fuzz test', function(assert) { - var vi = varint() - , expect + var expect , encoded - vi.on('data', function(data) { - assert.equal(expect, data, 'fuzz test: '+expect.toString(16)) - }) - for(var i = 0, len = 100; i < len; ++i) { expect = randint(0x7FFFFFFF) - encoded = varint.encode(expect) - - for(var x = 0; x < encoded.length; ++x) { - vi.write(encoded[x]) - } + encoded = encode(expect) + var data = decode(encoded) + assert.equal(expect, data, 'fuzz test: ' + expect.toString()) + assert.equal(decode.bytesRead, encoded.length) } assert.end() }) test('test single byte works as expected', function(assert) { - var num = [0xAC, 0x02] - var acc = varint() - - acc.on('data', function(data) { - assert.equal(data, 300, 'should equal 300 every time') - }) - - for(var i = 0, len = 10; i < len; ++i) { - acc.write(0xAC) - acc.write(0x02) - } - + var buf = new Uint8Array(2) + buf[0] = 172 + buf[1] = 2 + var data = decode(buf) + assert.equal(data, 300, 'should equal 300') + assert.equal(decode.bytesRead, 2) assert.end() }) test('test encode works as expected', function(assert) { var out = [] - assert.deepEqual(varint.encode(300), [0xAC, 0x02]) + assert.deepEqual(encode(300), [0xAC, 0x02]) assert.end() }) test('test decode single bytes', function(assert) { - var vi = varint() - , expected = randint(parseInt('1111111', '2')) - - vi.once('data', function(data) { - assert.equal(data, expected) - assert.end() - }) - - vi.write(expected) + var expected = randint(parseInt('1111111', '2')) + var buf = new Uint8Array(1) + buf[0] = expected + var data = decode(buf) + assert.equal(data, expected) + assert.equal(decode.bytesRead, 1) + assert.end() }) test('test decode multiple bytes with zero', function(assert) { - var vi = varint() - , expected = randint(parseInt('1111111', '2')) - - vi.once('data', function(data) { - assert.equal(data, expected << 7) - assert.end() - }) - - vi.write(0x80) - vi.write(expected) + var expected = randint(parseInt('1111111', '2')) + var buf = new Uint8Array(2) + buf[0] = 128 + buf[1] = expected + var data = decode(buf) + assert.equal(data, expected << 7) + assert.equal(decode.bytesRead, 2) + assert.end() }) test('encode single byte', function(assert) { var expected = randint(parseInt('1111111', '2')) - assert.deepEqual(varint.encode(expected), [expected]) + assert.deepEqual(encode(expected), [expected]) assert.end() }) test('encode multiple byte with zero first byte', function(assert) { var expected = 0x0F00 - assert.deepEqual(varint.encode(expected), [0x80, 0x1E]) + assert.deepEqual(encode(expected), [0x80, 0x1E]) + assert.end() }) function randint(range) {